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[Closed] Restoration of a possibly unique pre-war TV

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Brian Cuff
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Slowly, slowly, catchee monkey - I have at last got the metalwork back from the platers. The pictures show them as received. The finish is a bit blotchy but so much cleaner than the very rusty and pitted state it was in. The smaller components such as the screening boxes, choke clamps and other bracketry has come up very well.
I'm waiting for some fluid for my ultrasonic cleaner bath so that I can get most of the grime off the non-wound components. The front panel with its range of slider pots will benefit from a bath too! I just wonder whether a mist coat of acryllic "appliance" paint would help with the appearance of the main chassis!

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Posted : 21/03/2014 3:26 pm
freya
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I had always assumed that it would come back looking like new, is it the metals rough surface that causes the blotchy appearance ?
Looks much better though.

 
Posted : 21/03/2014 4:01 pm
Marc
 Marc
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Hi Brian,

For what it's worth, my point of view would be how happy would I be each time I saw the chassis ?
Even though no one else will see it I bet it would still nag a perfectionist like your self :aaq
So maybe a waft of appliance paint would be in order.

Marc

Marc
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Posted : 21/03/2014 4:09 pm
mark pirate
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I agree a bit of paint would make it look more uniform, I too thought it would have looked better after plating.

 
Posted : 21/03/2014 9:34 pm
Till Eulenspiegel
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When the chassis is populated with components the metal finish defects will not be as noticeable. The corrosion of the metal obviously had some effect on the plating process.

Till Eulenspiegel.

 
Posted : 21/03/2014 9:45 pm
Brian Cuff
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The chassis, in its original state had some really bad rust pitting, some vaguely rusted and some absolutely shiny surfaces (I thought that they were nickel plated but it turned out to be bright zinc) which had been under brackets etc. I know what you mean, Till, but I recon just of dusting with the acrylic aerosol will make that little bit of difference, especially on the back.

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Posted : 21/03/2014 9:53 pm
peterscott
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I just wonder whether a mist coat of acryllic "appliance" paint would help with the appearance of the main chassis!

Nah! Much better that it looks old and patinated.

Peter

www.nostalgiatech.co.uk

 
Posted : 23/03/2014 1:00 pm
Brian Cuff
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The owner of the set has decided that a mist coat of acrylic paint is the way to go and I must admit, it does look somewhat better!
A bit more progress - At last I have brought my ultra-sonic cleaner back into action. It holds 10L of solvent (I use "jewelery" grade) and what a difference it makes to the paxolin and Bakelite components. I have restored the two smoothing chokes (their clamps were zinc plated) and the picture shows these two components with a very unusual 2 wiper slider pot. The two sliders feed the RF and detector bias respectively. During dismantling, a three tags snapped off but fortunately, I have some eyelet tags which are almost identical to the originals so I was able to drill out the broken ones and replace them. Next is to rivet in the paxolin valve holders and bolt in the Bakelite ones - I don't want to risk cracking them.

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Posted : 25/03/2014 5:10 pm
Brian Cuff
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A bit more progress on the 12C today. After much searching for semi tubular rivets, I found some ideal tubular rivets so decided to use them. I turned a swaging tool out of silver steel to make a neat, rounded swage. I used silver steel as it can be hardened - but I didn't harden it as I had run out of Propane the last time I used the blow-torch and didn't replace the cylinder :bbd .
The pictures show all the valve bases and the screens dividing the grids from the anodes all riveted in place. The next step is to wait for some braided wire I have ordered so that I can start the wiring.

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Posted : 29/03/2014 10:11 pm
Brian Cuff
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The braided wire has arrived. I ordered some from 3 suppliers so that I can compare them. The only stuff that hasn't arrived is the push-back solid core wire from Radio Daze in the 'States. Using the tracking system, it says that my shipment has been "progressed through the office of exchange" whatever that means - probably that it's going to cost a lot in clearance fees :bbd .
I've started to wire the main chassis but am taking it very slowly as there are many opportunities to make mistakes and, as I like to make mechanical joints, there is a real risk of damage when trying to rectify errors.
One really annoying thing was that the field blocking oscillator transformer seems to have developed an O/C sync winding (I'm sure when I removed it, I chaecked it and it was OK!). Anyway, the sync winding is the outer of the three so I decided to use my new coil winder in anger. I de-lammed it and stuck it on the winder to unwind the faulty winding and count the turns at the same time - 600 in all. I had some 40swg enameled copper wire which was a fraction larger than the original but as it is the sync winding, I decided that it would be OK as long as there was enough room. As it turned out, I was 60t short of the 600 but as I said before, it's only a sync winding and I have bypassed these before and used a capacitor with success! At the same time as the rewind, I decided that I would change the appearance of the transformer which was obviously a replacement (see picture) and looked really out of place with its bright red PVC leadouts. I therefore made a tagboard which simply bolted onto the lugs which were present on the xfmr clamp frame - it looks so much better now (say)!
The other pictures show how the chassis looks so far. I know that most of the resistors are new but I have never met such a high percentage of resistors that are out of tolerance, most by at least 25% so they had to go!
As I write this, a parcel has just arrived from Radio Daze! No extra charges to pay so hooray for that and the wire is fantastic. It really looks the part and is so easy to use (thanks for the pointer, Cathy).

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Posted : 04/04/2014 11:47 am
Brian Cuff
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A bit more done! It's very slow work with the new braided wire as I have to superglue each cut end in order to stop the stuff fraying but it does look so much more in keeping with the age of the set. Even the push-back wire has a tendency to fray but I've found that if I use it as "pull-back" wire it's a lot better as the distortion of the sheath happens towards the middle of the connection being installed. The pictures show whats been done up to now - the time base section and smoothing/filtering are pretty well finished and I am now concentrating on the RF side. This is much more time consuming and is proving quite difficult but it is progressing. The front control panel with two rotary pots and nine slider controls is normally mounted on a separate metal assembly which bolts to the front of the main chassis. However, the mount for the CRT implosion guard is part of this assembly and, when in position, has two "sticky-up" things that prevent the chassis sitting upside down on the bench making it very difficult to wire. The panel had to be in position to get the wiring the right lengths when completed so I made a couple of cheeks for the rotary pots and stood the slider panel off the front of the chassis using 4BA studding. The pictures tell the story!

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Posted : 19/04/2014 8:42 pm
IJK2008
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Brian

Looking wonderful. How did you re-stuff the cardboard cased caps? I have one if these to do on a set.

Cheers

Ian

 
Posted : 19/04/2014 9:11 pm
Brian Cuff
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Hi Ian. One cardboard cap was missing and the other damaged so I had to make both complete assemblies. I sourced some card of the right thickness and used the old one, opened up, as a template. The metal fixing plate also had to be made. One of the things I did for these and the tubular caps was to buy a cheap (£14) mini deep fat fryer and some beeswax. The fryer is thermostatically controlled and can be set to under 100deg. so that the wax doesn't get too hot. One warning though: Don't buy the wax from a craft outlet but from an apiary supplier as it's much cheaper and available in 800g blocks.
After the caps were stuffed, I filled the "boxes" with wax and let them cool a bit and dipped them into the molten wax. The finish isn't perfect but looks the part. The LOPT was also filled with wax as I had to "decant" it to fit new lead-out wires.

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Posted : 19/04/2014 10:16 pm
Anonymous
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Beeswax?

It wasn't beeswax but Paraffin wax some place between candle and petroleum jelly. (You can mix the two actually to get it).

 
Posted : 19/04/2014 11:06 pm
peterscott
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Hi Ian. One cardboard cap was missing and the other damaged so I had to make both complete assemblies. I sourced some card of the right thickness and used the old one, opened up, as a template. The metal fixing plate also had to be made. One of the things I did for these and the tubular caps was to buy a cheap (£14) mini deep fat fryer and some beeswax. The fryer is thermostatically controlled and can be set to under 100deg. so that the wax doesn't get too hot.

Excellent! I love it! Must investigate a fryer for myself.

Peter :aad

www.nostalgiatech.co.uk

 
Posted : 20/04/2014 12:26 pm
Brian Cuff
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I did some more work on the RF section over the last couple of days and have succeeded in getting RF through it! I had to rewinding all 9 coils to lower the frequency to 45MHz by adding a turn or two to the originals. I kept to the original layout by lots of reference to the many pictures I took during the dismantling.
The first picture shows the strip without the screening cans fitted. These slide in between the 6 vertical screens to form a completely enclosed section for each bandpass coupling arrangement of two coils, inductively coupled.
The last RF stage drives the anode bend detector via a bifilar wound transformer. I was able to make rewinding easier by sourcing some ready made bifilar wire from a company called The Scientific Wire Company ( http://www.scientificwire.com ). This is a useful source of all sorts of “magnet wire” as enameled copper wire seems to be called now! They will supply small quantities which keeps the prices down.
The second picture shows the sweep of the RF section from aerial to CRT cathode It starts at 45MHz and finishes at 48.5MHz so the results so far are not too bad. The 9 cores to be tweaked make for an interesting exercise in patience and memory (that’s a bit of a blow for me!) because every adjustment seems to affect the waveform in some way but, more annoyingly, seems to affect the effect that the previous core made before! Anyway, I’m looking forward to increasing the gain while keeping a respectable bandwidth (needs, in theory, to be only 2.5MHz which seems to be the bandwith of most pre-war sets.

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Posted : 27/04/2014 12:42 am
Cathovisor
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The last RF stage drives the anode bend detector via a bifilar wound transformer. I was able to make rewinding easier by sourcing some ready made bifilar wire from a company called The Scientific Wire Company ( http://www.scientificwire.com ). This is a useful source of all sorts of “magnet wire” as enameled copper wire seems to be called now!

I blame the Merkins for that one...

The second picture shows the sweep of the RF section from aerial to CRT cathode It starts at 45MHz and finishes at 48.5MHz so the results so far are not too bad. The 9 cores to be tweaked make for an interesting exercise in patience and memory (that’s a bit of a blow for me!) because every adjustment seems to affect the waveform in some way but, more annoyingly, seems to affect the effect that the previous core made before!

Fairy Fingers! That's what you need! (Old BBC in-joke there)

 
Posted : 27/04/2014 3:11 am
Brian Cuff
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"Fairy Fingers"That's the term we used to use when setting up the afterglow panels on the old MK1 Cintel telecines. Stick a bit of destreak film in the gate and twiddle for hours. All controls interacted with all others - but not so many tweaks as for a delta-gun shadow mask tele!
The side racks of audio manipulation devices (flangers, graphic equalisers, echo devices etc. in editing and dubbing suites were called "Fairy Dust". It's a pity that fairy dust wasn't used during the editing of Jamaica Inn!

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Posted : 27/04/2014 9:09 am
Till Eulenspiegel
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Hi Brian,
That's a really good response curve. So the set is aligned to the upper sideband which means that there is a wide trough between the 41.5Mc/s sound carrier and the vision passband. I assume for that reason there are no sound rejector traps in the vision channel. Evidently when the AP transmitter was replaced by the VSB Crystal Palace transmitter many sets aligned to the upper sideband would not work properly.

Till Eulenspiegel.

 
Posted : 27/04/2014 10:19 pm
Brian Cuff
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You are correct (as usual) Till. There is a sound trap but not in the vision strip. The aerial plugs into a small metal box with two coaxes coming out of it, one to the vision RX and the other to the sound RX. There are two parallel tuned circuits in the box, one tuned to 41.5MHz and the other to 45MHz (now!) and these are used as traps as they are in series with the appropriate receivers' feeders. I'm surprised that that is enough rejection but it seems to be - the proof of the pudding is when I see a picture but I can see no sound on the video signal when I null it out. Normally, if there is any breakthrough, it can most easily bee seen on the sync bottoms!
I have just converted the sound receiver to 41.5MHz and will probably mount the re-wound mains transformer over the next few days so the rest of the metalwork and CRT can be mounted. Then comes the moment of truth :ccf :ccf .

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Posted : 27/04/2014 11:49 pm
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